Poly(arylene sulfides) (hereinafter abbreviated as “PASs”) represented by poly(phenylene sulfide) (hereinafter abbreviated as “PPS”) are engineering plastics excellent in heat resistance, chemical resistance, flame retardancy, mechanical strength, electrical properties, dimensional stability, etc. The PASs are commonly used in a wide variety of technical fields such as electrical equipments, electronic equipments, automotive equipments and packaging materials because they can be molded or formed into various kinds of molded or formed products, films, sheets, fibers, etc. by general melt processing processes such as extrusion, injection molding and compression molding.
As a typical production process of a PAS, is known a process in which a sulfur source is reacted with a dihalo-aromatic compound under heating conditions in an organic amide solvent such as N-methyl-2-pyrrolidone (hereinafter may also be abbreviated as “NMP”). As the sulfur source, is generally used an alkali metal sulfide, an alkali metal hydrosulfide or a mixture thereof. When the alkali metal hydrosulfide is used as the sulfur source, the alkali metal hydrosulfide is used in combination with an alkali metal hydroxide.
Since the polymerization of the PAS is conducted at a high temperature, a secondarily formed sulfur compound from the sulfur source and a decomposition product of the organic amide solvent that is a reaction solvent form the cause of occurrence of offensive odor.
Accordingly, the PAS formed by the polymerization is cleaned by, for example, washing a formed polymer separated from a liquid reaction mixture containing it with water, an organic solvent or a mixed solution of water and an organic solvent. However, the occurrence of offensive odor upon production of the PAS and upon molding or forming and processing thereof has not been completely inhibited even by such a washing treatment. In particular, when the dihalo-aromatic compound is reacted in an amount exceeding 1.00 mol per mol of the sulfur source, an unreacted dihalo-aromatic compound is taken in a PAS particle, and hydrogen sulfide derived from the sulfur source and a modified compound thereof are formed during a dehydration step or a polymerization reaction step, or a by-product which forms the cause of malodor is produced by a reaction of these compounds with an organic solvent used for washing, so that, in some cases, these may form the cause of occurrence of offensive odor upon production of the PAS or remain in the PAS to form the cause of occurrence of offensive odor upon molding or forming of the PAS.
In addition, since the liquid containing the organic amide solvent after the PAS is separated from the liquid reaction mixture containing the formed polymer or the washing waste liquid after the PAS is washed with the organic solvent or the like contains unreacted raw materials, a secondarily formed sulfur compound from the sulfur source and decomposition products of the organic amide solvent which is a reaction solvent and the organic solvent used in the washing which form the cause of occurrence of offensive odor, it has taken a lot of time and labor to conduct a deodorizing treatment for such a liquid to prevent the organic amide solvent or the like from recycling and reusing.
Thus, Japanese Patent Application Laid-Open No. 8-134216 (Patent Literature 1) has proposed a process for producing a PAS hard to cause corrosion of a mold upon molding by adding and reacting a 1,3-dihalobenzene after a reaction of a sulfide with a 1,4-dihalobenzene is substantially completed, thereby reducing an amount of a sulfur-containing gas produced upon heating and melting. Japanese Patent Application Laid-Open No. 2004-182840 (Patent Literature 2; corresponding to U.S. Patent Application Publication No. 2006/0052578) has proposed a production process of a PAS by keeping an NMP solution of a PAS after a polymerization reaction at 230 to 290° C. to conduct washing in a molten state and adding a silane coupling agent after the washing to conduct melt-kneading, thereby reducing a disulfide structure or a thiol structure in a resin.
Japanese Patent Application Laid-Open No. 2005-194312 (Patent Literature 3; corresponding to U.S. Patent Application Publication No. 2007/0161777) has proposed a production process of a PAS by washing a PAS obtained by polymerization with a hydrophilic organic solvent, such as acetone, containing 1 to 30% by mass of water to reduce a nitrogen content to 50 ppm or less based on the mass of the polymer, thereby markedly reducing a deposit on a mold or die upon melt-molding. Japanese Patent Application Laid-Open No. 2005-225931 (Patent Literature 4; corresponding to U.S. Patent Application Publication No. 2007/0093642) has proposed a production process of a PAS high in whiteness degree and excellent in melt stability by washing a polymer formed in a polymerization step with washing liquid composed of water, a hydrophilic organic solvent such as acetone or a mixed solution thereof repeatedly and then washing it with water or the mixed solution at a final stage to control a pH, thereby removing an organic amide solvent, an alkali metal halide, an oligomer, a decomposed product, etc. which are adhered to the PAS after a separation treatment. International Publication No. 2004/060973 (Patent Literature 5; corresponding to U.S. Patent Application Publication No. 2006/0086374) has proposed a production process of a PAS by washing a polymer separated from a liquid reaction mixture with an organic solvent such as acetone and then adding an inorganic acid such as hydrochloric acid to the organic solvent recovered to conduct distillation, thereby reducing the content of an alkaline compound such as methylamine.
According to all the inventions of Patent Literatures 1 to 5, however, the occurrence of offensive odor upon the production of the PAS and upon molding and processing thereof has been unable to be completely inhibited. When an organic solvent has been used for washing in particular, odor upon the production or odor upon the molding which is considered to be caused by a reaction product of hydrogen sulfide or a derivative thereof generated during a polymerization reaction with the organic solvent has been unable to be avoided. In addition, it has taken a lot of time and labor to conduct the deodorizing treatment for the remaining raw materials which are contained in the liquid containing the organic amide solvent after the PAS is separated from the liquid reaction mixture or the washing waste liquid after the PAS is washed with the organic solvent, and the secondarily formed sulfur compound from the raw material source and decomposition products of the organic amide solvent which is the reaction solvent and the organic solvent used in the washing which form the cause of occurrence of offensive odor.
On the other hand, Japanese Patent Application Laid-Open No. 11-228696 (Patent Literature 6; corresponding to U.S. Pat. No. 6,013,761) has proposed a production process of a poly(arylene sulfoxide) by weighing and pouring a hydrogen peroxide solution having a concentration of 30 to 100% into a PAS suspended in concentrated sulfuric acid to oxidize the PAS. Japanese Patent Application Laid-Open No. 2009-79317 (Patent Literature 7) has proposed a production process of paper composed of a PPS oxide (PPSO) by dispersing fine powder of PPS and short fiber of PPS in water, making paper from the resultant paper stock and then subjecting the resultant paper to a oxidation reaction treatment in the presence of a liquid containing 0.1 to 20% by mass of an oxidizing agent selected from an inorganic salt peroxide and aqueous hydrogen peroxide. Japanese Patent Application Laid-Open No. 7-3024 (Patent Literature 8; corresponding to U.S. Pat. No. 5,496,917) has proposed a two-stage oxidation method for a PAS by oxidizing a solid polymer in a suspension medium with ozone and reacting the resultant reaction product with hydrogen peroxide used in the form of an aqueous solution having a concentration of 30% in the presence of a catalytic amount of concentrated sulfuric acid in acetic acid.
However, the inventions of Patent Literatures 6 to 8 are directed to the production of the poly(arylene sulfoxide) or PPSO by oxidizing and modifying the PAS and not to a process for producing a PAS. Accordingly, according to such an invention, it has been impossible to produce a PAS that is an engineering plastic excellent in heat resistance, chemical resistance, flame retardancy, mechanical strength, electrical properties, dimensional stability, etc. and can be commonly used in a wide variety of technical fields such as electrical equipments, electronic equipments, automotive equipments and packaging materials by utilizing the property of the PAS that can be molded or formed into various kinds of molded or formed products, films, sheets, fibers, etc. by general melt processing processes such as extrusion, injection molding and compression molding. In addition, the inventions has involved a problem that since hydrogen peroxide or the like is used at a high concentration for oxidizing and modifying the PAS, it takes a lot of cost for a treatment step thereof or a post treatment for making hydrogen peroxide or the like remaining in a waste liquid after the treatment harmless.